Electrical timing apparatus



Feb. 17, 1959 R. w. SHIPMAN 2,874,281

ELECTBICAL TIMING APPARATUS I Filed Dec. 7, 1953 '2 Sheets-Sheet 1 INf ENTOR, Fa 14. fiizyxflalz United States Patent ELECTRICAL TIMING APPARATUS- Roy W. Shipman, Detroit, Miclh, assignor to Weltronic Company, Detroit, Mich., a corporation of Michigan Application December 7, 1953, Serial No. 396,585

12 Claims. (Cl. 250-27) This invention relates generally toelectrical timing apparatus which is particularly adapted, among other uses, as a sequence timer for a resistance welding, apparatus.

An object of this invention is to provide a new and improved timing network.

A further object of this invention is to provide such a network in which a pair of timing networks are concurrently charged and thereafter perform their timing functions in succession.

Another object of this invention is to provide in such a network a new and improved pulsing circuit for controlling the instant in the half cycle of the supplied potential at which certain of the network valves may be rendered conducting.

Another object of this invention is to provide a new and unproved interrelation between the energy flow controlling valves and the valve controlling. the termination providing a series of repeating operations thereof or for a providing single operation thereof in response to actuation of the initiating switch.

Other objects of this invention will be apparent from the specification, the appended claims, and the drawings, in which drawings:

Figures 1A and 1B schematically illustrate a preferred form of timing network embodying the invention;

Fig. 2 illustrates the operation of the pulsing circuit sub-combination; and, 1

Fig. 3 illustrates a modified form of pulsing circuit.

The invention is illustrated in a sequencing network 1 for performing the standard NEMA 5B type functions which are Squeeze Time, Weld Interval Time, Cool Time, Heat Time, Hold Time, and on Time. Alternating potential for actuating the network 1 is supplied from a transformer T1 having its primary, winding 2 connectible with asuitable source of alternating potential, as for example, a 440 volt 60 cycle supply, by means of the line switch LS1. One terminal 4 of the secondary winding 6 of the transformer T1 is continually connected to a bus B1 and selectively connected to a bus B2 by means of the start switch SW1 and the contacts CRlb of a relay CR1. The other terminal 8 of the winding 6 is continually connected to the bus B3.

A squeeze time network 10 controls the time interval between the closure of the start switch SW1 and the initiation of conduction of thyratron IV. A weld interval timing network 12 controls the time interval between the time that thyratron 1V conducts and the conduction of thyratrons 2V and 3V to terminate the "weld interval period. A hold time network 14 controls the time interval between the initiation of conduction of the thyratrons 2V and 3V and the conduction of thyratron 4V to terminate the hold time period.

This period permits the: weld nugget to solidify. prior to withdrawal of the welding electrodes E from the workpiece W. An off time network 16 controls the time interval between the initiation of conduction of the thyratron 4V and the re-initiation of the thyratron '5V to start a subsequent operation.v

The heat and cool time periods are. controlled by a multivibrator network 18. including the heat time'controlling network 20 and the cool time controlling network 22 which control the rate at which the thyratrons 6V and 7V alternately conduct during the weld time interval. During the. nonconducting time period of thyratron 6V (conducting time. period of thyratron 7V); the back-to-back or reversedly connected thyratrons 8V, and 9V will conduct each, cycle of the voltage supplied through the line switch LSlto energize. the'transiormer T7. When energized, transformer T7 overrides the blocking bias. applied to the firing thyratrons, 10V and 11V respectively whereby they conduct to fire the ignitrons 12V and 13V. When conductive, the ignitrons 12V and 13V energize the welding transformer T3 to supply energy to the welding electrodes E. Closure of the switch SW5 will reduce the weld time interval below the heat time interval and the network will provide only asingle heat interval as determined by the net.- work 20. a

In the present embodiment, the anode of the thyratron. 1V is connected through normally open contacts CRZa. of the control relay CR2, a single-repeat switchfSWZ. (shown in open or repeat position), an emergency stop switch SW3, tov the bus B2. The common terminal 24 of the. switches SW2 and SW3 is connected through the. energizing winding 26 of the control relay CR1 to the anode of the thyratron 5V, the cathode of which is connected to the bus B3. The anode of the thyratron 1V is. also connected through the energizing winding 28 of the control relay CR2 to the bus B3 while the cathode of the thyratron 1V is continually connected to thev bus B3- through a resistor R1 and selectively connected to the bus B2 through the normally open contacts CRlc of the relay CR1.

One terminal 30 of the squeeze time network 10 is connected through the usual current limiting resistor to, the control grid of thethyratron 1V and the other terminal 32 thereof is connected to a common terminal 34 intermediate a pair of series connected resistors R2 and R3; The free terminal of the resistor R2 is connected to the bus B1 while the free terminal of the resistor R3 is connected through a resistor-capacitor network 36 and a resistor R4 to the bus B3. When the contacts CRlc are open, the potential of the cathode of thyratron 1V is substantially that of the bus B3 and the network 10 charged by gridccnduction of the thyratron 1V. When contacts CRlc close, the potential of this cathode is made that of bus B3 and the potential appearing across the network 10 as well as that'appearing across the resistor R2 is applied between the control grid and cathode of thyratron 1V. The resistor R2 superimposes a relatively low magnitude A. C. component on the blocking potential established by the network 10 to provide. moreaccuracy to the squeeze timing function. Also the. potential across resistor R2, when acting alone, will provide a firing potential to insure that an otherwise slow-to-fire" tube conducts when desired.

The anode ofthe thyratron 4V is connected to bus;

B3 through a conductor 38, the oif time network 16 and resistor R4. The conductor 38 connects with one terminal 4%) of the, off time network 16 and the other terminal 42 of this network is connected to terminal 44 which is intermediate theresistor R4 and the network 36.

3 to bus B2 and can only conduct when the thyratron 2V is conducting. The control grid of this thyratron is connected through a grid current limiting resistor, network 14 and resistors R3 and R2 to bus B1. The potential appearing-across the resistors R2 and'R3 provide an alternating control potential superimposed upon the potential established by the -hold time" network 14 for controlling the delay between the firing of thyratron 2V and the firing of the thyratron 4V. Likewise, the potential appearing across the resistor R4 provides an alternating potential superimposed upon that of the off time network 16 for controlling the thyratron 5V.

The thyratrons 2V and 3V are connected in back-toback or anti-parallel relationship between the buses B2 and B3 through the transformer T4. More particularly, the anode of thyratron 2V and the cathode of thyratron 3V are connected through a resistor-capacitor network 46 and the primary winding 48 of the transformer T4 to the bus B3 while the anode of the thyratron 3V and cathode of the thyratron 2V are connected through the normally open contacts CRZc to the bus B2. The control grid of the thyratron 2V is connected through the weld interval timing network 12 to the terminal 34 and serves to control the time interval between the closureof contacts CR2c and the firing of thyratron 2V.

The control grid of the thyratron 3V is connected through resistors R5 and R6 and network 46 to the cathode of the thyratron 3V. An alternating biasing potential is normally applied across the resistor R6 by means of the transformer T5 having its primary winding connected between the busses B1 and B3. The phasing of the potential supplied by the transformer T5 with respect to that applied between the anode and cathode of the thyratron 3V is such that whenever this anode is positive with respect to this cathode and the network 46 is deenergized a negative grid-to-cathode potential will be maintained across the resistor R6. When, however, the thyratron 2V conducts during the half. cycle preceding the half cycle in which the anode of thyratron 3V is positive with respect to its cathode, the network 46 will be energized and the potential established thereacross will overcome that established across the resistor R6 and the thyratron 3V will conduct each half cycle subsequent to the half cycle in which the thyratron 2V conducts.

The transformer T4 has a center tapped secondary winding 51, the end terminals of which are connected through rectifiers 53 to the negative terminal 52 of the resistor R7. The center tap connection is connected to the positive terminal 54 of resistor R7. One terminal 52 of the resistor R7 is connected through the usual grid current limiting resistor to the shield grid of the thyratron 7V and the other terminal 54 thereof is connected through the resistors R8 and R9 to the common cathode connection 56 of the thyratrons 6V and 7V. Therefore when transformer T4 is energized, its rectified output establishes a blocking .bias potential across the resistor R7 which overcomes the conducting potential peaks which are otherwise supplied to thyratron 7V by the resistors R8 and R9. The shield grid to cathode circuit of the thyratron 6V does not include the resistor R7 and is uninfluenced by the energization of the transformer T4. The grid is connected through the usual current limiting resistor and the resistors R8 and R9 to the common cathode connection 56 whereby this grid will be brought to a conducting bias once each alternate half cycle of the voltage applied through the switch LS1.

The anode of the thyratron 7V is connected to the positive bus B4 through the normally open contacts CR2d and resistors R10, R11,'and R12 and the anode of thyratron 6V is connected to this -bus through resistors R14 and R15. The cathodes of these thyratrons are connected to a common cathode connection 56.

.The positive bus B4 and cathode connection 56 are energized by rectifying the output of the transformer T6. More specifically, bus B4 is connected to'the end termiacross the resistors R8 and R9 (to. be more clearly set 4 nals 58 and 60 of the secondary winding 62 of transformer T6 through the rectifiers 64 and 66, resistor R13 and capacitors C1 and C2. The center tapped terminal 68 of the winding 62 is connected by conductor 70 and branch conductor 72 to the common cathode connection 56. Capacitors C1 and C2 which are connected in series relation in shunt with the resistor R13 stabilize the direct current potential between the bus B4 and the cathode connection 56.

A commutating capacitor C3 is connected between the anodes of the thyratrons-6V and 7V to provide for a momentary change in anode-cathode potential of the conducting one of the thyratrons 6V or 7V upon the initiation of conduction of the other thereof to extinguish the previously conducting thyratron upon conduction of the other thereof as is well known in the art.

The pair of timing networks 20 and 22 hold the thyratrons 6V and 7V, respectively, blocked for a predetermined time interval subsequent'to' conduction of the other thereof. The network 22 comprises a capacitor C4 having a discharge circuit which includes the variable resistorR16, resistor R17, and resistor R18. During standby periods of the network 1, the normally closed contacts CRld are closed and shunt out the variable resistor R16 to insure-a rapid discharge of the capacitor C4. During operation of the network 1, however, the contacts CRld remainopen and the rate of discharge of the capacitor C4 will be primarily controlled by the setting of the resistor R16. One terminal 74 of the capacitorC4 is connected to the bus B4 through the series connected resistors R14 and R15 connected in parallel with the series connected resistors R18 and R19. The other terminal 76 of the capacitor C4 is connected through a current limiting resistor to the grid ofthe thyratron 7V. During the nonconducting period of thc' thyratron 6V, the potential of terminal 74 will be sub-v stantially that of the positive bus B4 and-the, capacitor C4 will charge due to the flow of grid current through the thyratron 7V. Upon conduction of the thyratron.

6V, the terminal 74 (which is then positive with respect, to the terminal 76) is connected through the thyratron 6V to the commoncathode connection 56 to place a blocking bias potential .between the grid and cathode of the thyratron 7V to maintain this thyratron blocked until the capacitor C4 has discharged to a predetermined low value, after which the thyratron 7V will berendered conducting at an instantv determined by the. potential out below) provided, however, that the transformer T4 is not energized. V V 4 The heat time network 20 comprises the capacitor C5 having one terminal 78 connected through the series connectedresistors R10, R11, and R12 .to the bus B4 having in parallel therewith the series connected resistors R20 and R21. The other terminal 80 is connected through a grid current limiting resistor to the control grid of thyratron 6V. A discharge circuit for the capacitor C5 extends from terminal 80 through variable resistor R22 and resistor R20 to the other terminal 78. With this arrangement, the capacitor C5 will be charged by grid current flow of the thyratron 6V during the periods in which the thyratron 7V is blocked but when the thyratron 7V conducts, the terminal 78 is effectively connected to the commoneathode connection 56 and the capacitor" C5 will provide a blocking bias potential between the grid and cathode of thyratron 6V for a time period pri marily dependent upon the magnitude of the resistor R22. The blocked period of the thyratron 6V, as will;

be hereinafter set forth, determines the time period in Which'the transformer T3 in energized to supply Welding potential to the electrodes E. The blocked or non conducting time period of the thyratron 7V likewise determines the cool time period or intervening interval in which the transformer T3 is not energized to supply potential to the welding electrodes E;

I '[tshould be noted that the resistor R11 is connected;

in series between. the shield .grid and cathode of thethyratron 2Vl The direction of the potential. established thereacross, when thethyratron 7V conducts (indicating the occurrence of a heat period), is such as to establish a blocking bias between the shield grid and cathode of the thyratron 2V and prevents thyratron 2V from conducting during a heat period even though the weldinterval timing network 12 times out. This interrelationship between the thyratrons 2V and 7V insures a complete heat period each time that the electrodes E are energized.

Instandby. condition, the contacts CR2d will be open to interrupt the anode circuit of the thyratron 7V and the thyratron 6V will continually conduct. The continual conductionof thyratron 6V maintains apotential across the resistor R which is applied as a blocking bias potential between the grid and cathode of the thyratron 8V to keep this thyratron blocked. More specifically, the grid of the thyratron 8V is connected through. the usual current limitingresistor to the common terminal 82 of the resistors R14 and R15 while the cathode thereof is connected through the bus B2 to the common terminal 84' between the resistors R11 and R12. The grid-cathode circuit is completed through the resistor R12 and bus B4 to the other or upper terminal of the resistor R15. When thyratron 6V conducts, thyratron 7V will be blocked and the potential appearing across resistor R15 will block the thyratron 8V; When, however, the th'yratron 6V blocksand' the thyratron 7V conducts, thepotential across the resistor R12 will act to apply a conducting bias between the grid and cathode of the thyratron 8V to insure that it conducts. V

The thyratrons 8V and 9V are connected in antiparallel relationship with each other and in series with the primary winding 88 of a transformer T7 between the busses B2 and B3 through a resistor-capacitor network 86', and a weld-no weld switch SW4. It will be recognized that the grid-cathode circuit for the thyratron 9V is similar to that explained above in connection with the thyratron 3V so that the thyratron 9V trails the conduction of thyratron 8V and unless the thyratron 3V conducts the thyratron 9V will remain blocked.

Thetransformer T7 is provided with secondary windings 90 and 92'. The winding 90 is connected between the grid and cathode of the firing thyratron 10! through a biasing network 94 whilethe' winding 92 is connected between the grid and cathode of the firing thyratron 11V through a biasing network 96 The networks 94 and 96 maintain the firing thyratrons 10V and 11V blocked so long as the transformer T7 remains deenergized. The potential established bythe windings'90 and 92, with the transformer T7 energized, is of such magnitude and phase asto overcome the blocking bias established by the networks 94 and 96 to cause the firing thyratrons 10V and 11V to conduct during the half cycles in which their respective anodes are positive with respect to their cathodes. Whenconducting, the thyratrons 10V and 11V trigger the ignitrons 12V and 13V respectively in a manner well known in the art.

The transformer T3 may be of the Hipersil'type or may be power factor corrected by use of a series capacitor and the network 98 containing the resistors R8 and R9 is arranged to provide for firing the thyratrons 6V and 7V at a predetermined point in the voltage wave applied between the main busses B5 and B6. The transformer T3 is connected in series with the back-to-back ignitrons 12V and 13V between these busses B5 and 136..

The particular phase angle at which the thyratron 7V will conduct is controlled by'means of the phase-shifting,

network 100. This network, as illustratedgis of the usual type in which a resistor R24 and a capacitor C6 are series connected between the 'end terminals 58 and 60 oi phase shift imparted to the potential appearing between tive magnitudes of the resistor R24 and capacitor C6.

35" 2(.b) by the line Eps.

The conductor connects the center tap 68 with one terminal'104 of the primary winding 106 of transformer T8. The other terminal 108 of this winding is connected by conductor 110 to the terminal 102. At present it seems preferable to arrange the values of resistor R24 and capacitor C6 to provide for firing the thyratron 7V at substantially the point in the half cycle of voltage in which the bus B5 is positive with respect to the bus B6, and for this purpose the network is adjusted to phase shift the voltage applied to the winding 106 so that it lags the voltage between the busses B5 and B6 by 90'". The transformer T8 is provided with a center tapped secondary winding 112 having a center tap 114 and end terminals 116 and 118. The common terminal 120 of the resistors R8 and R9 is connected to the center tap 114-. The. other terminal 122 of the resistor R8 is connected through a capacitator C7 to the terminal 116 while the other terminal 124 of the resistor R9 is connected through a rectifier 126 to the terminal 118. The terminal 116 is connected through rectifier 128 to the terminal 124. This arrangement provides a direct current pulsating voltage across the resistor R9 which pulsates onces each half cycle of the voltage appearing between the busses B5 and B6. An alternating voltage will appear across the resistor R8 which is phase shifted from that appearing across the winding 112 by an amount depending upon the relative magnitude of the resistors R8 and capacitor C7 and in this instance is 90 degrees leading. The potential applied between the buSsesBS and B6 is represented in Fig. 2(a) by the line E1. The phase shifted output potential of the network 100 is represented in Fig. The rectified pulsating potential appearing, across the resistor R9 is represented in Fig. 2(c) by the line Er9. The phase, shift alternating potential appearing across the resistor R8 is illustrated in Fig. 2(d) by the line Er8. The wave Eg in Fig. 2(e) illustrates the potential appearing between the terminals 124 and 122, which is applied between the shield grid and cathode of the thyratron 6V. The potential wave Eg will be applied between the shield grid and cathode of the thyratron 7V but during the period in which the transformer T4 is energized this will be lowered with respect to the horizontal zero line so that the high peaks of the wave Eg will not be of sufiicient magnitude to render the thyratron 7V conducting. From a study of Fig. 2 is will be apparent that by phase shifting the output voltage of the phase-shift network 100, the peaks of wave Eg may be made to occur at any desired inter val in the voltage wave B1.

In Fig. 3 there is shown a modified form of peaking network 98a which may be used to provide the same wave shape Eg, Fig.2(e), which is provided by the networks 98 and 100. This network eliminates the need for phase shifting the voltage applied to the transformer T811 and the primary winding 106a thereof may be connected directly to the potential supplying busses 135a and 36a. The transformer T81: is provided with a first secondary winding 130 having output terminals 132 and" 134. Connected between the terminals 132 and 134 are a pair of circuits each containing a resistor and a capacitor. The resistor R26 has its free terminal connected to the terminal 132 and the free terminal of its associated capacitor C8 is connected to the terminal 134. The resistor R27 of the other circuit has its free terminal connected to the terminal 134 while the free terminal of itsv associated capacitor C9 is connected to the terminal 132. The common connection 135 between the capacitor C9 and resistor R27 of the phase circuit is connected to the common connection 133 between the resistor R26 and capacitor C8 by a pair of resistors R28 and R29. The resistor R28 has connected in series cir-.

cuit therewith a rectifier 136 while the resistor R29 has; connected-inv series circuit therewith a rectifier 138, The

, 7 rectifier 136 is connected to conduct current in a-direction opposite to the direction in which the rectifier 138 conducts.

The common terminal 140 between the rectifier 136 and resistor R28 is connected through a second secondary winding 142 of the transformer TSa to the terminal 150 connected to the cathode of a thyratron 14V while the common terminal 144 of the resistor R29 and rectifier 138 is connected through a resistor R30, rectifier 148 and normally open switch SW to the terminal 150. A timing network 146 and current limiting resistor is connected between the grid of the thyratron-14V and terminal 152 of rectifier 148. By proper selection of the values of the resistor R27 and capacitor C9, and the relative values of the resistor R26 and capacitor C8, the potential appearing across the resistors R28 and R29 may be made to, correspond to the voltage wave Eps, Fig. 2(b), when the voltage supplied by the winding 130 corresponds to the wave E1, Fig. 2(a) The voltage appearing across the resistor R28 corresponds to alternate ones of the loops Er9, Fig. 2(c), while the voltage appearing across the resistor R29 corresponds to the intervening loops of the curve-E19. The potential supplied by the winding 142 corresponds to the potential wave Er8, Fig. 2(d). When these are combined together, the sumniation will correspond to the curve Eg, Fig. 2(a), and this wave is applied to the rectifier 148. The rectifier 148 is polarized to permit substantially unimpeded conduction of the portion of the wave Eg appearing below the zero axis thereof but imposes a high impedance to the flow of the, portion of the wave which appears above the zero line. The potential appearing across the rectifier 148 is represented by the voltage pips Ega 'asshown in Fig. 2(f). It will be apparent that the voltage appearing across the rectifier 148 is added to that appearing across the timing network 146 and the potential placed between the grid and cathode of the thyratron 14V is in the form of a capacitordischarge curve in which there is superimposed the voltage pips Ega. The magnitude of these pips Ega is so chosen with respect to that of the discharge curve of the network 146 that the thyratron 14V will be rendered conducting in the half cycle of the voltage in which the bus B5a is positive with respect to the bus B6a at an instant determined by the occurrence of the voltage pips Ega.

It is believed that the remaining details of construction may best be understood by a description of operation of the apparatus, which is as follows:

In normal standby condition, the line switch LS1 is closed energizing the busses B5 and B6 and the transformer T1. When energized, the transformer T1. energizes the busses B1 and B3 to supply energizing potential for charging the squeeze time network 10, the weld interval timing network 12, and the hold time network 14. Energization of the busses B1 and B3 also e nergize the blocking bias producing transformers T5 and.

T2 for the thyratrons 3V and 9V respectively and the transformer T6 which supplies the direct potential between the bus B4 and connection 56. With the transformer T6 energized, the network 98 will be energized and the thyratron 6V will conduct. It 'will further be appreciated that all of the anode-cathode circuits for the valves 1V through 9V except 6V and 7V are connected between the busses B2 and B3. Since bus B2 is disconnected from the transformer T1 by the normally open start switch SW1 and the normally open contacts CRlb of the relay CR1, all of thesethyratrons therefore, are in a normally nonconducting condition. Thyratron 7V cannot conduct since its anode circuit is open through contacts CRZd. The firing thyratrons 10V and 11V while having their anode circuits connected between the busses B5 and B6 are prevented from conducting and firing the ignitrons 12V and 13V by the blocking bias establishing networks 94 and 96;; When it is desired to initiate a weld, the switch SW1" as rmsi" is closed to connect the bus B2 to' the terminal 4 of the transformer TI. This establishes a potential between busses B2 and B3 and current then flows through the winding 26 of the relay CR1 through the thyratron 5V in a circuit which extends from the bus B2 through the normally closed emergency stop switch SW3, winding 26, anode to cathode of the thyratron SV to the bus B3. Upon energization, the relay CR1 closes its contacts CRla to complete a circuit for the usual ram mechanism (not shown) for moving the electrodes E against the workpiece W. Closure of the contacts CRlb completes a holding circuit about the switch SW1 which may now be opened without interfering with the cycle then in process. In repeating operation, the switch SW1 will be held closed until the desired number. of weld spots have been initiated. Closure of the contacts CRlc completes the circuit form the cathode of the thyratron 1V to the bus B2 thereby completing the biasing circuit through the squeeze time network 10and the resistor R2 for the thyratron IV. This closure of the contacts CRlc also effectively transfers the potential of the cathode of the thyratron 1V from that of the bus B3 to that of the bus B2 thereby terminating further charging of the squeeze time network 10 and permitting it to discharge. Opening of the contacts CRld opens the shunt circuit about the resistor R16 of the cool time network 22.

At the end of a predetermined squeeze time inter val as determined by the rate of discharge of the network 10, the thyratron 1V conducts to complete a circuit between the busses B3 and B2 through the energizing winding 28 of the relay CR2, the anode-cathode of the thyratron 1V, and the now closed contacts CRlc. Upon energization, the relay CR2 closes its contacts CR2a without effect since it is now assumed that the single-repeat switch. SW2 is in its open position for repeat operation. Closure of the contacts CR2c completes the anode-cathode circuits for the thyratrons 2V and 3V between the busses B2 and B3 and completes the grid to cathode biasing circuit for the thyratron 2V whereby the potential established across the weld interval timing network 12 is applied as a biasing potential between the grid and cathode. This also terminates further charging of the network 12 to permit it to discharge to time the weld interval. Opening of the contacts CR2b opens the circuit through resistor R31 to line B3 and reduces the current which would otherwise be drawn thereby were the connection maintained. Closure of the contacts CR2d completes the anode circuit for the thyratron 7V which thereupon commences to conduct and blow out the thyratron 6V at the next peak .Eg. This results in energization of the resistor R12 and deenergization of'the resistor R15 to remove the blocking bias from and to provide a conducting bias potential between the grid and cathode of the thyratron 8V. Thyratron 8V thereupon fires and thyratron 9V trails to energize the transformer T7 which overcomes the blocking bias potential on the firing thyratrons 10V and 11V which fire to fire the ignitrons 12V and 13V. When the ignitrons fire, the transformer T3 is energized with alternating potential to energize the electrodes E for applying welding current to the workpiece W.

At the end of the heat time as determined by the network 20 a voltage peak of the wave Eg will fire the thyratron 6V which blows out the thyratron 7V whereby the blocking bias potential is re-established on the thyratron 8V. Thethyratron 7V is held blocked for the duration of cool time by the network 22. At the end of cool time, the next voltage peak of the curve Eg will cause the thyratron 7V to re-conduct and establish a a heat time period, the resistor R11 will. be energized to provide a blocking bias potential between the shield grid and. cathode of the. thyratron. 2V to prevent this thyratron from firing eventhough the weld interval timing; network 1'2" should time out duringlsuch aheat period. At the end of the weldtime intervahthe network. 12 will have'timed outto remove the blocking bias potential between the gridland' cathode of the thyratron 2V. If this occurs during a heat time period the thyratron ZV'will not conductuntil the end of the heat time then'in progress. If such time out occurs during a cool time, thyratron 2V wi1l immediately conduct. When thyratron 2V conducts thyratron 3V trails and these thyratrons complete a circuit between the husses- B; and B?" through. the now. closedcontacts CRZc, the thyratrons 2V and 3V, the resistor-capacitor network 46, and transformer T4, applying run cycle potential to the transformer T4. When energized, the transformer T4- estahlishes a direct current bias potential across the re- 'sist'or R7 which overrides the peakiiig conducting pips of the voltage wave Ega to prevent further. firing of the thyratron 7V. Thyratron. 7V'heingthus preventedfrom firing, thyratron 6V continues to conduct to maintain thyratrons- 8V and'9V blocked;

Conduction of the thyratron ZVconnects the cathode of the thyratron 4V to the bus 31- whereby holdtime network is connected between the gridand cathod e of thyratron 4V and further charging of this network 14 is prevented. Network 14 begins to time out and at the end of the hold time the thyratron 4V conducts to rapidly charge the bit time network 16. When charged the network 16 places a blocking bias potential between the grid and cathode of. the thyratron V to block the same for deenergizing the winding, 26 of the relay CR1.v When deen'ergized, the relay CR1 opens its contacts CRIa, CRIb and CRlc, and closes its contacts CRld. Opening. of the contacts CRla dee'nerg'iz'es the ram mechanism for moving the electrodes E' away from the work W. Opening of the contacts CR'i'b opens the circuit in shunt with the switch SW1 which, if the switch SW1 is still closed as now assumed, is without effect. Opening of the contacts CRIc'disconnects the cathode of thyratron 1V from the bus B2 and terminates further conduction of'this' thyratron. When thyratron 1V stops conducting, the energizingwinding' 28'of the relay CR2 is no longer energized and the contacts CRZa, CRZc andCRZ'd openand' contacts-CRZ'B close. Opening of the contacts CRZa is with- I out efiect sihce in the conditions stated the single-repeat switch SWZis in its open or repeat position. Opening of the contacts CRZc disconnects the; cathodeof the thyratron 2V and anode of thyratron 3V from the bus B2 thereby terminating further conduction of these thyratrons; Closing of the contacts CRZb connects the cathode. of the thyratron 2V through a resistor R31 to the bus B3 thereby permitting the weld interval timing network 12 to charge by grid conduction in the thyratron 2V. Opening of the contacts CRZd opens the anode circuit of the thyratron 7V preventing this thyratron from again conducting. Termination of conduction of the thyratron 2V terminated the conduction of the thyratron 4Vwhi'ch terminated further flow of charging current to the ofi time network 16, which network then begins to time out; At the end of ofi time the network 16 has sufficiently' discharged to permit the thyratron 5V to re-conduct to initiate a subsequent cycle as above described, provided however, that the switch SW1 has remained closed. If, at the time the thyratron FV was blocked to deenergize the relay CR1, the switch SW1 waszopen, the opening of the contacts CRlb would immediately open the anodecatho'de circuits of all the thyratrons 1V, 2V, 3V, and 4V, permitting the networks in, 12 and id tore-charge and the network 16 to immediately start discharging, after which a re-closure of th'e switch SW1 would initiate a sub"- sequent'operatio'n as described above.

lithe switch SWZsis in its closed position for single operation irrespectiveoi the, time interval in which the the thyratron 1V and ithe. busBZ through the emergency stop switch SW3. which is in shuntwith the circuit through the thyratron 1V and the contacts CRlc. With this arrangement, once the relay CR2 becomes energized it will remain energized until the concurrent opening of the switchSWl and contacts. CRlb, thereby preventing the opening of the contacts CRZc to terminate conduction of the thyratrons 2V, 3V and 4V so that the off time networks 16 continues to be charged and to maintain the thyratron 5V blocked. The relay CR1 cannot become deenergized' until the switch SW1 is opened.

It will be appreciated that, if desired, the network 98:: may be used in place of the network 98la1id the potential established between the terminals 150 and 152' which will have the. same wave shape as that established'between' the terminals 122 and 124, may be substituted therefor. In Fig 3, however, this potential is applied across a' rectifier 148 and combined with a potential established by a timing network 146 to control the thyratron 14V. In normal operation, alternating potential is' applied be-' tween the busses 135a and Baa. The thyratron 14V will, however, not conduct due to the open condition of the normally open switch SW5. Since the cathode of the thyratron 14V is connected to the bus B511 through a resistor R32 and the grid' of the thyratron 14V is con nected through the network 146 and rectifier 148- to the bus 136a, the capacitor of thc'network 146 willbe charged due to grid current flow through the thyratron 14V. When the switch SW5 is closed, the potential of the oath ode of the thyratron 14V is transferred from substantially that of the bus 135a to that of the bus Boa and the potential across the network 146'is applied as a blocking bias potential between the grid and cathode of the thyratron 14V and further flow of charging current to the net'- work 146 is terminated to permit it to discharge. Thepotential established by the network 98a is applied across the rectifier 143 which is in a polarity such that the rectifier easily passes all of the portion of the wave Eg below the zero axis leaving only the voltage pips Ega appearing thereacross due to the network 98a. These are superimposed on the normal discharge curve of the network 146 and when the network 146 has sufliciently discharged, one of these pipswill bias the thyratron-14V into conduction at a given point inthe half cycle of the voltage wave inwhich bus 135a is positive with respect to bus Boa whereby the thyratron 14V conducts to energize the lead 154 connected between the bus B5aand the anode of the thyratron 14V.

While there is shown and described herein certain preferred forms of the invention, it is to be distinctlyund'erstood that many modifications thereofmay be made with-- in the scope of the invention and the scope of the invention is to be determined by the scope of the herein after appended claims.

What is claimed and is desired to be secured by United States Letters Patent is as follows:

1. Ina control combination for energizing a load from an alternating potential source, an initiating means for initiating a how of energy to such load from such source, means for controlling said fiow including a pair of valves and including means for rendering said valves alternately conducting and nonconducting in sequence and a control device for normally preventing one of said valves from conducting, said one valve having a control electrode anda cathode, a peaking network, a-circuit connecting said network between said control electrode and said cathode and normally effective to supply a critical potential therebetween ata selected instancezin the voltage cycle of said source, biasing means in said circuit and effective 'in a. first condition to prevent ,the application of said critical potential, a normally nonconductive valve having,

switch SW1 is maintained closed the initial conduction an: anode and a cathode and, apair of control electrodes,

one of said control electrodes and said cathode of said last-introduced valve and etfective at they end of a predetermined time interval to apply a critical potential therebetween, a voltage producing device connected with said anode and cathode of said one valve, circuit means connecting said voltage device between the other of .said control electrodes and said cathode of said last-introduced valve whereby conduction of said one valve is effective to place a blocking potential between said other control electrode and said cathode of said last-introduced valve, means responsive to the conduction of said last-introduced valve for rendering said biasing means in its said first condition, and means responsive to said initiating means for rendering said control device ineffective and said timing network effective to time out said predetermined time interval.

2. In a timing system, a pair of terminals for energization from an alternating potential source, a plurality of electric valves each having an anode and a cathode and a control electrode, means including a normally open switch connecting said cathode of a first of said valves to a first of said terminals, means including an impedance component connecting said cathode of said first valve to the second of said terminals, means including the winding of a relay connecting said anode of said first valve to said second terminal, a plurality of timing networks, each said network comprising a capacitor and a resistor connected in parallel, means connecting a first of said timing networks between said first terminal and said control element of said first valve, means connecting said anode of a second of said valves to said second terminal, means connecting said anode of a third of said valves to said second terminal, means connecting said just-mentioned anode to said cathode of said second valve, means including normally open contacts of said relay connecting said cathode of said third valve to said first terminal, means connecting a second of said timing networks between said first terminal and said control electrode of said second valve, means connecting a third of said timing networks between said first terminal and said control electrode of said third valve, and means including an impedance component connecting said cathode of said third valve to said second terminal.

3. The combination of claim 2 in which said means which connects said anode of said second valve includes a fourth of said timing networks, means connecting said anode of a fourth of said valves to said first terminal and including an actuator for said normally open switch, means connecting said cathode of said fourth valve to said second terminal, and means connecting said fourth timing network between said cathode and said control electrode of said fourth valve.

. 4. In a timing network, first and second terminals adapted to be energized from an alternating potential source, third and fourth terminals adapted to be energized from a direct potential source and arranged to have said third terminal positive with respect to said fourth terminal, a plurality of electric valves each having an anode and a cathode and a control electrode, means connecting said first terminal to said anode of a first of said valves and including an energizable device, means connecting said cathode of said first valve to said second terminal, means connecting said anode of a second of said valves to said second terminal and including an energy storage time delay network, means connecting said control electrode of said first valve to a point in said just-mentioned means which is intermediate said justmentioned delay network and said anode of. said second valve, means connecting said cathode of said second valve to said anode of a third of said valves, means .con-

delay network, means connecting said cathode of said third valve to said second terminal and including an impedance component, means connecting said just-mentioned cathode to said first terminal and including a normally open switch, means connecting said control electrode of said. third valve to said first terminal and including an energy storage time delay network, means connecting said anode of a fourth of said valves to said third terminal and including an impedance component, means connecting said anode of a fifth of said valves to said third terminal and including an impedance component, said third valve having a second control electrode,

means connected between said second control electrode.

and said cathode of said third valve and including a portion of said just-mentioned impedance component, a timing circuit connected between said anode of said fourth valve and said control electrode of said fifth valve, a shunting switch for said last-named circuit, means for actuating said shunting switch in response to a change in energization of said energizable device, a peaking network connected to be energized from said first and second terminals and having an output circuit connected between said control electrode and said cathode of said fifth valve and effective to periodically render said fifth valve in a conductive conditions, means responsive to the conductive condition of said third valve to render said peaking network ineffective to render said fifth valve conductive, and circuit means connecting said grid and said cathode of a sixth of said valves across said component associated with one of said fourth and said fifth valves.

5. In a timing network, first and second terminals adapted to be energized from an alternating potential source, third and fourth terminals adapted to be energized from a direct potential source and arranged to have said third terminal positive with respect to said fourth terminal, a plurality of electric valves each having an anode and a cathode and a control electrode, means connecting said first terminal to said anode of a first of said valves and including an energizable device, means connecting said cathode of said first valve to said second terminal, means connecting said anode of a second of said valves to said second terminal. and including an energy storage time delay network, means connecting said control electrode of said first valve to a point in said just-mentioned means which is intermediate said justmentioned delay network and said anode of said second valve, means connecting said cathode of said second valve to said anode of a third of said valves, means connecting said control electrode of said second valve to said first terminal and including an energy storage time delay network, means connecting said cathode of said third valve to said second terminal and including an impedance component, means connecting said just-mentioned cathode to said first terminal and including a normally open switch, means connecting said control electrode of said third valve to said first terminal and including an energystorage'time delay network, means connecting said anode of a fourth of said valves to said third terminal and including an impedance component, means connecting said anode of a fifth of said valves to said third terminal and including an impedance component, said third valve having a second control electrode, means connected between said second control electrode and said cathode of said third valve and including a portion of said just-mentioned impedance component, a timing circuit connected between said anode of said fourth valve and said control electrode of said fifth valve, a shunting switch for said last-named circuit, means for actuating said shunting switch in response to a change in energization of said energizable device, a peaking network connected to be energized from said first and second terminals and having an output circuit connected between said control electrode and said cathode of said fifth valve and effective to periodically render said fifth valve in a conductive condition, a sixth of said valves connected in anti-parallel with said third 13 valve, connections between said third valve and said cathode and said control electrode of said sixthjvalve for rendering said sixthvalve conductifigin trailing relatiohship 'to said third valve, a transformer having a pri mary winding connected between .said first and second terininals through said anodes and cathodes of said third and said sixth valves whereby said transformer ,is ener gized in response to the conductive condition of said third and sixth valves, an impedance network connected to said peaking network and effective when energized to render said peaking network ineffective to render said fifth valve conductive, said transformer having an output winding, circuit means connecting said output'wiuding across said impedance network, and circuit means connecting said grid and said cathode of a seventh of said valves across said component associated with one of said fourth and said fifth valves.

6. The combination of claim in which a rectifying network is inserted in said circuit means which connects said output winding across said impedance network.

7. The combination of claim 6 in which said fifth valve has a second control electrode, a timing circuit connected between said anode of said fourth valve and said second control electrode of said fifth valve, and a commutating capacitor is connected between said anodes of said fourth and said fifth valves.

8. In a timing network, first and second terminals adapted to be energized from an alternating potential source, third and fourth terminals adapted to be energized from a direct potential source and arranged to have said third terminal positive with respect to said fourth terminal, a plurality of electric valves each having an anode and a cathode and a control electrode, means connecting said first terminal to said anode of a first of said valves and including an energizable winding of a first relay, means connecting said cathode of said first valve to said second terminal and including an impedance device, means connecting said cathode of said first valve to said first terminal and including normally open contacts of a second relay, means connecting said anode of a second of said valves to said second terminal and including an energy storage time delay network, means con-' necting said cathode of a third of said valves to said second terminal, means connecting said anode of said third valve to said first terminal and including an energizing winding of said second relay, means connecting said control electrode of said third valve to a point in said means which connects said anode of said second valve tov said second terminal which is intermediate its said delay network and said anode of said second valve, means connecting said cathode of said second valve to said anode of a fourth of said valves, means connecting said control electrode of said second valve to said first terminal and including an energy storage time delay network, means connecting said cathode of said fourth valve to said second terminal and including an impedance component and normally closed contacts of said first relay, means connecting said just-mentioned cathode to said first terminal and including normally open contacts of said first relay, means connectingsaid control electrode of said fourth valve to said first terminal and including an energy storage time delay network, means connecting said anode of a fifth of said valves to said third terminal and including an impedance component, means connecting said anode of a sixth of said valves to said third terminal and including an impedance component, said fourth valve having a second control electrode, means connected between said second control electrode and said cathode of said fourth valve and including a portion of said justmentioned impedance component, a timing circuit connected between said anode of said fifth valve and said control electrode of said sixth valve, a shunting switch for said last-named circuit, said shunting switch comprising normally closed contacts of said second relay, a peaking network connected to be energized from said first and second terminals and having an output circuit ,con-

nected between said control electrode and said cathode of said sixth valve and effective to periodically render said sixth valve in a conductive condition, means responsive to the conductive condition of said fourth valve to render said peaking network'ineifective to render said sixth valve conductive, and circuitmeans connecting'said grid and said cathode of a seventh of said valves across said component associated with one of said fifth and said sixth valves.

9. In a system for controlling the duration of the application of a pulsating energization of a load circuit such as welding electrodes, a pair of electric valves each having an anode and a cathode and a pair of control electrodes, a pair of potential supplying terminals for energization from a source of direct potential, a first anode circuit including a first impedance network connecting said anode of a first of said pair of valves to the positive one of said terminals, a second anode circuit including a second impedance network connecting said anode of the second of said pair of valves to said positive terminal, a connection between each of said cathodes and the negative one of said terminals, a first capacitor connected between said first anode circuit and a first of said control electrodes of said second valve, a second capacitor connected between said second anode circuit and a first of said control electrodes of said first valve, a phase-shifting network having an output circuit, a transformer connected to said output circuit, a plurality of impedance elements connected between the second control electrode and said cathode of said first valve, blocking means for establishing a potential across a first of said impedance elements in a polarity tending to hold said first valve nonconducting, circuit means including a portion of said transformer for uuidirectionally and pulsatingly energizing a second of said impedance elements in a polarity tending to hold said first valve nonconducting, means including a reactive component connecting the third of said impedance elements across a portion of said transformer, a commutating capacitor connected between said anode circuits, and circuit means connecting said second and said third impedance elements between the second of said control elements and said cathode of said second valve.

10. The combination of claim 9 in which there is a third valve having an anode and a cathode and a pair of control electrodes, a circuit connected between one of said control electrodes and said cathode of said third valve and including a portion of said first impedance network, said just-mentioned portion being arranged to provide a blocking bias potential to said third valve at one conductive condition of said first valve, means responsive to the conduction of said third valve for controlling said blocking means to prevent further conduction of said first valve, and a biasing circuit connected between the second of said control electrodes and said cathode of said third valve.

11. In a timing network for timing a pair of timing functions, a pair of terminals for energization from a source of electrical energy, a pair of electric valves each having an anode and a cathode and a control electrode, a first circuit means including an impedance connecting said anode of a first of said valves to a first of said terminals, a second circuit means connecting said cathode of said first valve to the second of said terminals, a third circuit connected in shunt with said first circuit impedance and in series with said first valve, said third circuit including the second of said valves, a first energy storage timing network connected between said control electrode of said first valve and said second terminal, a second energy storage network connected between said control electrode of said second valve and said second terminal, and switch means in said second circuit between said cathode of said first valve and said second terminal.

l2.'The combination of claim 11 in which an irn- References Cited in the file of this p atefit UNITED STATES PATENTS Blaich Jan. 15, 1935 Knowles Aug. 9, 1938 Bivens Sept. 26, 1944 Bivens Feb. 27, 1945 England May 23, 1950 Apr- 22, 1952 Auger Dec. 23, 1952 Vaughan Jan. 6, 1953' Elliot Oct. 20, 1953 Czaja Apr. 20, 1954 

